Automatic merge from submit-queue

Expand documentation and TODOs in a few packages

I was reading through unfamiliar code and mostly added TODOs and expanded and clarified documentations.

There are a couple of things that are real code changes:
- Removed some unused constants
- Changed `workqueue.Parallize` to clamp the number of worker goroutines to the number of items to be processed.
- Added another unit test to `workqueue.queue`.  I thought I found a bug (I was wrong) and wrote a unit test to isolate.  I figure the extra test is worth keeping.